Atomic order, electron structure, and critical parameters of epitaxial YBaCuO films

X-ray structural and optical methods were applied to make a detailed invest igation of atomic and electronic structure of superconducting YBa2Cu3O7-del ta films obtained by pulsed laser deposition. Optical transmission spectrum was found to depend not only on intraband ((h) over bar omega < 1.2 eV) an d interband (h omega > 1.95 eV) transitions, but also on contributions from charge transfer transitions O 2p double right arrow Cu 3d in the dielectri c phase due to local order in a system of crystallographic (11l) planes. Su perconducting properties of the films are determined by orientational struc tural transition (00l)+(11l)double right arrow(00l) and by Anderson type tr ansition from a charge transfer O 2p double right arrow Cu 3d insulator to a strongly degenerate semiconductor with metallic conductivity. We show the effects of ordering on transition temperature T-c and demonstrate that at the concentration of (00l) clusters below the percolation threshold (20%) t he behavior of T-c has catastrophic character. (C) 1999 American Institute of Physics. [S0003-6951(99)01239-5].